This invention relates to an optical system for a coherent light illuminating source which is used for effecting an optical recording such as a hologram.
Where a hologram is recorded, it is known to cause parallel light rays from a coherent light source to be passed through a diffusion plate so as to illuminate a subject. In this method, a bad influence due to mars and dirt and dust is restricted and the concentration of a light on a low frequency component can be avoided in a Fourier transform holography. As a result, a better recording can be performed. If, however, it is necessary to reduce the F-value of an optical system, speckle noises due to a diffusion illumination are superposed on a reproduced image with the consequent low resolution.